I need to do something similar, but I don't seem to find the Euclidean distance tool.
I have a polygon which represents a riverbed area and I would like to make a buffer based on the river width.
So I am wondering if the proposed procedure is suited to achieve what I am trying to do.
The buffer would be n*width with n an integer number I choose. If you look at the picture you see that the buffer would be larger at the width1 cross-section, and it would be thinner at the width2 cross-section.
I tried using the percentage buffer tool, but with no luck.
I also tried applying a buffer with a geometry expression such as
but "width" is not a characteristic of "geometry", so no luck here either.
Probably the best way to do this is to draw some cross-section (e.g. one each 10-50 m), calculate the width and build kind of a skeleton of your river as you do for instance in HECRAS.